Djokovic moved a step closer to a third championship at Flushing Meadows and 14th Grand Slam title overall by eliminating Millman 6-3, 6-4, 6-4 to get to the tournament's semifinals for an 11th appearance in a row.
While second favourite Rafael Nadal [3.65] dragged himself through almost five hours and was kept playing until almost three in the morning to win his quarter-final, Djokovic has dropped only two sets since the start of the tournament. "But we saw him a couple of nights ago", said the 31-year-old Serb.
"Before that I've got Davis Cup which I'm also really jumping out of my skin to team up with the boys there, and anytime you get to play for your country is an unbelievable opportunity". I have to take at least 10 shirts for every match.
After Millman held serve to make it 2-1 in the second, Djokovic complained even more during a side change.
Millman has learnt to deal with such appalling bullying but says it can be distressing for players.
American player Nicole Gibbs told CNN past year that she'd first started receiving online abuse while playing college tennis.
"I was struggling. He was struggling", Djokovic said.
"I didn't even know the rule", said Millman, whose request to leave briefly was permitted based on something called the "Equipment Out of Adjustment" provision in the International Tennis Federation guidelines, because his sweat was making the court slippery.
"It's fantastic to have the roof but it feels like a sauna".
Djokovic was given a time violation warning and double-faulted to offer Millman a break point opportunity before losing his first serve after running down the shot clock a second time. But, you know, I think that with so many players retiring that first round, first day or second day, and so many players struggling to breathe, especially on the center court, which, you know, doesn't, there is no circulation of the air at all, especially court level.
Djokovic, grateful for a bit of a breather, sat grinning in his chair with his shirt off, much to the crowd's amusement.
The Wimbledon 2018 champion Novak Djokovic has not lost a set since the round of 64.
"He doesn't miss a lot himself, so he just runs left, right, gets a lot of balls".
"I really have respect for him".
But, not to be denied, Djokovic broke straight back to take the match to enhance his flawless semi-final record in NY to 11 from 11.
"I don't think that's a normal occurrence", John Isner said on Tuesday after his quarterfinal loss to Juan Martin del Potro. She won the Indian Wells Open and made it to the fourth round of the Australian Open.
But the 13-times major winner's class ultimately told, gaining a decisive break in each set to advance to a last-four meeting on Friday with rejuvenated 2014 runner-up Kei Nishikori.